The invention relates to a device for preventing the overfilling of a fuel tank provided with a filler neck and a filling vent line, an operational vent line, which leads to the outside or to a collecting tank, opening into the fuel tank above the opening into the filling vent line, in which operational vent line there is connected a valve device which is closed during filling of the fuel tank and is open in the remaining time.
A device of this type is disclosed in EP 0 464 420 or DE 43 43 498. In the known devices, the valve device for the operational vent line is fastened laterally at the upper end of the filler neck, and is displaced into the closed position via a valve actuating member, which projects into the end of the filler neck, by the fuel-pump nozzle, inserted for the filling-up, or by a filler neck closure flap which is knocked against by said fuel-pump nozzle. This solution is mechanically complicated and complicated to produce. In International Application No. PCT/AT 97/00177, which is not a prior publication, from the same applicant, a substantially simpler device with a design which is favorable in terms of cost has therefore already been proposed, in the case of which the valve device has a valve closing member which can be engaged with a valve seat in the direction leading away from the fuel tank, is preloaded into the open position and is bridged, at least in the blocked state, by a flow-restricting partial-flow path.
This type of valve device is a component which is completely separated from the end of the filler neck and is actuated solely by the operating pressures and/or gas flows which occur, and this does not require a complicated mechanical coupling with the engaging fuel-pump nozzle or the closure flap, or pressure diaphragm. The flow restriction in the partial-flow path is selected to be so large that the overpressure building up in the end phase of the filling-up in the tank space above the opening of the filling vent line is not substantially reduced within that time period in which an average user would be tempted to refuel. It is therefore ensured that the tank space above the filling vent line is not significantly filled up with fuel during refueling. Only some time after the conclusion of the refueling operation is the pressure slowly reduced via the partial-flow path, as a result of which any fuel from the filler neck runs back into the tank while slightly filling the tank space above the opening of the filling vent line. As soon as the pressure gradient via the partial-flow path undershoots a prescribed value, the valve device opens and releases a substantially larger flow cross section than the partial-flow path, this flow cross section permitting normal aeration and ventilation during operation. No noteworthy gas flow occurs via the valve device during driving operation, with the result that said valve device remains open and renders it possible for pressure fluctuations in the interior of the tank to be immediately compensated via the large flow cross section of the valve device.
If strong heating of the fuel occurs directly during the refueling operation, this is also accompanied by strong outgassing of the fuel, which in some circumstances cannot be reduced quickly enough via the partial-flow path. It is the object of the present invention to improve said device to the effect that such a dangerous overpressure situation can also be excluded. This object is achieved according to the invention by means of the features included in the characterizing part of Claim 1.
In this way, when the pressure drop across the partial-flow path becomes too large, the pressure relief valve clearance is opened and, to be specific, in a very simple way by virtue of the fact that the valve closing member working against the valve seat overcomes the preloading force of the latter. This creates a pressure relief valve function which reliably prevents the exceptional overpressure situations described.
In accordance with an advantageous embodiment of the invention, it is proposed that the valve seat is constructed in the form of a sleeve whose inner side serves for bearing the valve closing member and whose outer side serves for bearing against the inner shoulder, and which is preloaded by means of a compression spring against the inner shoulder and the valve closing member. This structure permits the device to have a design which is particularly compact and operates exclusively axially and thus without being susceptible to faults.
If strong heating of the fuel occurs directly during the refueling operation, this is also accompanied by strong outgassing of the fuel, which in some circumstances cannot be reduced quickly enough via the partial-flow path. It is the object of the present invention to improve said device to the effect that such a dangerous overpressure situation can also be excluded. This object is achieved according to the invention by virtue of the fact that, for its part, the valve seat is movably mounted, forms a pressure relief valve clearance with an inner shoulder of the valve device, and is preloaded into the closed position and in the direction of the valve closing member.
In this way, when the pressure drop across the partial-flow path becomes too large, the pressure relief valve clearance is opened and, to be specific, in a very simple way by virtue of the fact that the valve closing member working against the valve seat overcomes the preloading force of the latter. This creates a pressure relief valve function which reliably prevents the exceptional overpressure situations described.
In accordance with an advantageous embodiment of the invention, it is proposed that the valve seat is constructed in the form of a sleeve whose inner side serves for bearing the valve closing member and whose outer side serves for bearing against the inner shoulder, and which is preloaded by means of a compression spring against the inner shoulder and the valve closing member. This structure permits the device to have a design which is particularly compact and operates exclusively axially and thus without being susceptible to faults.
A further preferred embodiment of the invention is distinguished in that the partial-flow path is formed by grooves, notches or the like in the surface of the valve closing member and/or of the valve seat. This constitutes a particularly simple way of setting up the partial-flow path.
In any case, it is particularly advantageous when the valve closing member is preloaded into the open position by its dead weight or by spring loading. This constitutes a particularly simple possibility of implementing closure of the valve device above a prescribed threshold value in a fashion controlled by pressure and/or flow.
A further aspect of the invention resides in the creation of a valve device for a device of the type described above and characterized by a valve closing member which can be engaged with a valve seat, is preloaded into the open position and is bridged, at least in the blocked state, by a flow-restricting partial-flow path, the valve seat for its part being movably mounted, forming a pressure relief valve clearance with an inner shoulder of the valve device, and being preloaded into the closed position and in the direction of the valve closing member.